Decoherence and entropy generation in an open quantum scalar-fermion system with Yukawa interaction

We have studied the decoherence mechanism in a fermion and scalar quantum field theory with the Yukawa interaction in the Minkowski spacetime, using the non-equilibrium effective field theory formalism appropriate for open systems. The scalar field is treated as the system whereas the fermions as the environment. As the simplest realistic scenario, we assume that an observer measures only the Gaussian 2-point correlator for the scalar field. The cause of decoherence and the subsequent entropy generation is the ignorance of information stored in higher-order correlators, Gaussian and non-Gaussian, of the system and the surrounding. Using the 2-loop 2-particle irreducible effective action, we construct the renormalised Kadanoff-Baym equations, i.e., the equation of motion satisfied by the 2-point correlators in the Schwinger-Keldysh formalism. These equations contain the non-local self-energy corrections. We then compute the statistical propagator in terms of the 2-point functions. Using the relationship of the statistical propagator with the phase space area, we next compute the von Neumann entropy for the system. We have obtained the variation of the entropy with respect to various relevant parameters. We also discuss the qualitative similarities and differences of our results with the scenario when both the system and the environment are scalar fields.Comment: v2, 24pp, 7 figs; Added references and discussion, results unchanged; Accepted in EPJ

Arthroscopic anterior cruciate ligament reconstruction with central quadriceps tendon bone (CQTB) graft: An outcome study in fifty Indian patients

Background: Arthroscopic ACL reconstruction using biologic autografts is the current gold standard in the management of symptomatic ACL tears. The commonly used BPTB (Bone-Patellar Tendon-Bone) and quadrupled hamstring tendon grafts have their own disadvantages. This study was conducted to evaluate the efficacy of CQTB (Central Quadriceps Tendon Bearing) graft as an autograft for ACL reconstruction in relieving instability in ACL deficient knees.Methods: 50 patients (45males; 5 females) with symptomatic ACL laxity, who underwent arthroscopic ACL reconstruction using the CQTB graft were followed up for 1 year. The functional improvement was analyzed by comparing the pre-operative Lysholm scores with those at 03 months, 06 months and 12 months post operatively. The objective improvement was analyzed comparing the Anterior Drawer and Lachman test grades pre-operatively and after 1 year follow up. The mean length of the graft and the post-operative morbidity were also noted.Results: The average Lysholm scores improved from a pre-operative value of 44.34 to 78.98,87.86 and 91.58 at 03months,06 months and 1 year respectively. (p<0.05; ANOVA). The number of patients with Grade I, II and III laxities on Anterior Drawer test improved from 01, 36 and 12 respectively to 43, 06 and 01 respectively 1 year after surgery (p<0.05; paired t test). The number of patients with Grade I, II and III laxities on Lachman test reduced from 1, 34 and 15 y to 39, 10 and 01 respectively. The average thickness of graft harvested was 9.21mm.Conclusions: CQTB autograft is a viable option along with other available autografts in its ability to reconstruct native ACL, without any hazards and additional complications